I've participated in the Reidan service a couple of times, and would like to be more familiar with it than I am. I keep meaning to contact one of the ministers who are trained in it, but I am far away from both of them.

This is just my impression. That lineage seems to have tapped into Japanese ascetic traditions. For instance, they are the lineage that started the 100 day aragyo practice which enables priests to conduct kito blessings. I understand it's now practiced widely in Nichiren Shu. Japanese asceticism is probably best exemplified by yamabushi who combine Buddhism, particularly tantric Buddhism with indigenous mountain religion. Tendai has a close association with yamabushi practice and they have a well known kaihogyo practice on Hiei which clearly draws on Yamabushi influence. I believe the ascetic traditions also include reidan type practices.